Which of the following compounds is a tribasic acid?

$A$ metal $(X)$ dissolves in both dilute $HCl$ and dilute $NaOH$ to liberate $H_2$ gas. Addition of $NH_4Cl$ and excess $NH_4OH$ to an $HCl$ solution of $(X)$ produces $(Y)$ as a precipitate. $(Y)$ is also produced by adding $NH_4Cl$ to the $NaOH$ solution of $(X)$. The species $(X)$ and $(Y)$,respectively,are:

The element that does $NOT$ exhibit allotropy is$-$

Discuss the general characteristics of Group $15$ elements with reference to their electronic configuration,oxidation state,atomic size,ionisation enthalpy and electronegativity.

On heating,compound $(A)$ gives a gas $(B)$ which is a constituent of air. This gas,when treated with $H_{2}$ in the presence of a catalyst,gives another gas $(C)$ which is basic in nature. $(A)$ should not be:

Which of the following statements is true?